Liposomes have been used as a delivery vehicle for sustained release of drugs, both in parental and topical applications (Weiner et al., J. Pharmaceutical Sciences, 74:922 (1985); Norley, et al., J. Immunol., 1365:681 (1986)).
It is important that the rate of drug release from liposomes is slow with respect to the speed of the drug action. Ideally, zeroth-order release kinetics is needed for this purpose. In order to retard the drug release from liposomes, the present invention of "solid core liposomes," wherein a polymeric matrix, with or without embedded colloidal gold particles, is encapsulated in the interior aqueous compartment of a liposome, was developed.
Release of drugs, particularly proteins and polypeptides, from the "solid core liposomes" will be significantly retarded to achieve an improved sustained release kinetics.